1. Field of the Invention
The present invention relates generally to a method for fabricating dielectric devices including ferroelectric devices applied to, for instance, capacitors, pyroelectric infrared detectors and the like, and particularly to a fine patterning technology of dielectric substances.
2. Description of the Prior Art
With the recent progress in the developments of non-volatile memory tips, microsensors, actuators and the like, importance of fine pattern etching technologies applied to dielectric substances represented by the ferroelectric substances have become increasing. Known fine pattern etching methods for Si-dielectric substances and electrode materials include dry processes such as reactive ion etching using a reactive or etching gas, sputter etching and the like, and wet processes such as chemical etching. Investigations have been made on the patterning of the ferroelectric substances represented by lead titanate (PbTiO.sub.3), PZT (lead-zirconium titanate) and PLZT (lead-lanthanum-zirconium titanate), and electrode materials of noble metals such as Pt, Au, Pd and the like, or compounds thereof, by the reactive ion etching and sputter etching categorized as the dry processes.
The above-mentioned materials however have a low reactivity with the etching gas and thus demonstrate a low etch rate, and therefore there is a need to rise the temperature of a sample up to several hundred degree centigrade (M. R. Poor and C. B. Fleddermann: Journal of Applied Physics, 70 (6), p.3385-3387 (1991)).
On the other hand, the sputter etching uses accelerated argon ions or the like to cause a physical collision of the ions with a sample thereby to effect anisotropic etching. This results in a lesser role of chemical reaction and thus this method appears effective for the patterning of the ferroelectric substances.
Separate from this, an investigation is also conducted on the patterning of the ferroelectric substances represented by perovskite ceramics containing Pb by the chemical etching method as the wet process. The chemical etching has advantages such as a high etch rate and a lower cost of the equipment used for the process. Chemical etching, however, is disadvantageous in that because the etching processed by the chemical etching is isotropic which often accompanies side etching, the reproducibility of the pattern becomes rather poor due to the side etching.
In the above-mentioned reactive ion etching process, the etch rate of the ferroelectric substance is low because it has only a low reactivity with the etching gas, and a ratio of the etch rate of the material to that of the photoresist (selective ratio) is also small. Therefore, devices configured with the ferroelectric substance, in particular, those having a film thickness of the ferroelectric substance of several .mu.m, such as pyroelectric device and piezoelectric device, require more than one hour for the etching process. Thus, the reactive ion etching process suffers from a disadvantage that the photoresist layer is completely removed by the etching by the end of the process of etching on the ferroelectric substance film. As a result, the ferroelectric substance film is damaged and the device cannot demonstrate a satisfactory performance.
In the processes of the sputter etching and the reactive ion etching, since an electrode of an etching equipment is usually insulated from a sample to be etched by a quartz plate having a thickness of several mm, cooling efficiency of cooling water on the rear face of the electrode is not satisfactory. As a result, the processes suffer from a disadvantage that the photoresist layer is sometimes baked down by a rise in the sample temperature.
In order to cope with this problem, a means is taken for raising the cooling efficiency by applying a vacuum grease between the sample and the electrode. The application of the grease however takes much time and has problems such as outflow of the grease if the area of the sample is small, and possible contamination by the grease.
In the method of chemical etching of the ferroelectric substances represented by perovskite oxide, the conventional process of using only the known etchant has a problem of a residue on the substrate or the electrode. The method also has the disadvantage of poor reproducibility of the pattern due to possible side etching, forming a pattern with a tapered cross-sectional shape.